“The Days Between” is a story that appears as the second chapter of the novel Coyote, written by American science fiction writer Allen Steele. It tells of a man, Gillis, who lives all alone on a spaceship for 32 years—the other crew members being in an extended state of deep sleep or biostasis—and then dies in a random accident, 198 years before the ship will arrive at the planet Coyote. This paper begins from a Heideggerian interpretation of Gillis’s existential condition, and then argues that Gillis’s unique existence presents a challenge to Heidegger’s grounding assumption of a being-in that constitutes both Dasein and its world. In the conclusion, the potential role of science fiction as a literary genre is discussed in relation to Heidegger’s own thinking about technology and art, with the suggestion that science fiction may be needed today for its power, a saving one likely, to elicit a responsible response to the pervasive technological instrumentalization.